The present invention relates to a system for monitoring the condition of a tire.
German Published Patent Application No. 196 38 280 describes a method and a device for generating an error signal in a motor vehicle having at least two wheels located on the right and left in the front and rear areas of the vehicle. This is accomplished by detecting signals that represent the rotational velocities of the vehicle wheels. In particular, cornering is also detected as a function of the detected signals. The signals detected during cornering are then compared with a setpoint performance present during cornering, whereupon the error signal is generated as a function of the comparison. The comparison makes it possible to detect faulty speed sensor signals, for example, due to line reversal.
A system for detecting a status of the wheels of a motor vehicle is known from German Patent No. 197 12 097. This is accomplished by providing an arrangement for generating speed signals representing the rotational movements of the wheels, and an evaluation arrangement that is used to output a signal as a function of the generated signals, representing a display-relevant status. The main idea of German Patent No. 197 12 097 is that the evaluation arrangement is designed so that first difference values for the speed differences of at least two vehicle wheels on the two vehicle sides are first formed as a function of the generated speed signals. The signal representing a display-relevant status is then output as a function of a first comparison of the formed difference values with each other and/or with predefinable first threshold values.
The present invention relates to a device for monitoring the condition of tires on the wheels of a motor vehicle, an arrangement for detecting the rotational movements of the wheels being provided.
A tire that has become detached from the rim jeopardizes the safety of the vehicle driver:
The detached tire places the vehicle in an unfavorable state. For example, this may be expressed by the vehicle swerving. Detecting a detached tire enables a vehicle dynamics control system to be switched to a special mode that makes it possible to reduce this risk. For example, a defective rear wheel may be depressurized when braking.
The present invention requires a vehicle having an arrangement for detecting the rotational movements of the wheels and generating first quantities that are dependent on the rotational movements detected. The present invention also requires a comparison arrangement in which at least one comparison involving at least one of the first quantities is carried out. An evaluation arrangement is also provided in which a signal is output as a function of the output of the at least one comparison.
The comparison is advantageously preceded by a sorting operation in which at least two of the first quantities are sorted by value. A detached tire is detectable as a function of the signal output by the evaluation arrangement.
The vehicle is advantageously a vehicle that is equipped with an wheel slip control system.
The wheel slip control system is advantageously designed as a vehicle dynamics control system.
In specific system states of the vehicle dynamics control system, the generation of the first quantities advantageously involves a transformation. As a result, the quantities represented by the signals of the arrangement for detecting the rotational movements are transformed onto a common point.
The present invention is advantageously characterized by the fact that, if the vehicle dynamics control system is fully ready for operation or fully active, the first quantities correspond to the wheel speeds that have been transformed onto the center point of a vehicle axle. However, the first quantities may also be proportional to the wheel speeds that have been transformed onto the center point of a vehicle axle. If a vehicle dynamics control system is present, this requires little additional expense, since these quantities are already present in a vehicle dynamics control system.
Since the first quantities have already undergone sorting, the first quantities of the two vehicle wheels whose first quantities have the two highest values may be advantageously compared with each other in a comparison.
A difference between two of the first quantities is formed in at least one further comparison.
If the vehicle dynamics control system is fully ready for operation or fully active or in passive mode, the number of comparisons carried out in the comparison arrangement is then advantageously incremented by one if the comparison arrangement determines that the wheel, whose corresponding first quantity has the highest value, is a driven wheel. In the subsequent, further comparison, the brake pressure specified by the driver is advantageously compared with a limit value. When driving the vehicle on a xcexc-split roadway, one lane of which is icy, for example, the driven wheel located in the icy lane may spin and thus have a much higher wheel speed. To prevent this situation from erroneously resulting in the detection of a detached tire, the additional condition of the brake pressure is advantageously introduced.
In vehicle dynamics control systems, the brake pressure specified by the driver is frequently measured by the admission pressure sensor between the reversing valve and the main brake cylinder. The reversing valve is the valve that switches mainly between a driver-dependent and a driver-independent braking mode. Other positions of the pressure sensor in the hydraulic circuit are, of course, also conceivable. The important thing is that the pressure there is a measure of the brake pedal actuation executed by the driver.
If the vehicle dynamics control system is not fully ready for operation or not fully active, the brake pressure specified by the driver is compared advantageously with a threshold value in the comparison arrangement.
The vehicle dynamics control system that is not fully ready for operation or not fully active, and not simultaneously in passive mode, is characterized by the fact that at least the anti-lock function is ready for operation or active.
It is advantageous if the evaluation arrangement detects a detached tire if the output of all comparisons carried out in the comparison arrangement continuously indicates a detached tire for a period exceeding a predefinable minimum time period. This eliminates short-term peak values of individual first quantities.
The detection of a detached tire results in the vehicle dynamics control system advantageously switching to a special mode.